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  #1  
Old February 28th 2012, 16:33
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Brake pedal travel

Quick question,

Those of you running 4 pots all round - how is your pedal travel?

I am running 996 calipers all round with the stock 19mm M/C - all bled up nicely but i seem to have a lot of pedal travel. This is kind of understandable but was considering runnings 2 psi residual pressure valve - is anyone else doing this?

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Deano
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Old February 29th 2012, 14:47
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I found the stock m/c just about OK for road use but I suspect with some harder use it would have been too much and the pedal would have bottomed out. I don't think the valves would make too much difference, have you thought about using a Mk2 golf m/c? They are a straight 20.64mm diameter IIRC and should do a better job with a slightly higher pedal effort but less travel.
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Old February 29th 2012, 16:00
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Is the mk2 golf one a straight swap?

sounds like mine is the same as yours - brakes lock out but if i was to really stamp on the brakes the pedal would bottom out.

When doing bit of research i came accross a couple of people complaining about pedal travel with CB front and rear discs and had to use the RP valve which apparently made the pedal better.
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Old February 29th 2012, 17:25
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If you don't mind a little bit of fitting, I'd suggest a balance bar dual-M/C setup. I have a CNC drop-down setup on mine, but there are floor mount ones though for buggies (Wilwood, etc.) which may work in that small space. I run 924T brakes all around (the same as N/A 944/928) and must have adjusted it at least half a dozen times until I was happy with the front to rear bias. It essentially wound up because close to balanced front to rear. I started out with most of the bias up front and kept doing runs and adjusting until the fronts wouldn't lock up any more (FWD cars have a lot of weight shift up front, our cars not as much--I'm guessing all the weight in the rear of a bug just shifts to the middle of the car in a stop). I don't the idea of bias valves to the rear circuit because you're essentially 'limiting' the full potential of the M/C to that circuit.

My pedal travel is low and feels as solid as a Mercedes.
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Old March 1st 2012, 03:43
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Thanks for your input - essentially i would have been better off with a fully adjustable sytem like that......unfortunately i am too far along my build to be changing something like that without major hassle. It would be a good last resort though
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Old March 1st 2012, 15:00
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Quote:
Originally Posted by dub_crazee View Post
Is the mk2 golf one a straight swap?
Yes, just need to use bolts with nuts as the m/c is not threaded like a bug one..
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Old March 1st 2012, 17:18
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...that's interesting - once ive finally taken my bug on a road test - if im not happy il give that a go!

Thanks Ricola!
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Old March 5th 2012, 11:28
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I have 944 single pots at the front and 928S4 4 pots at the rear with a hydraulic handbrake in series with the rear line. I found that the rear line was allowing too much flex within the handbrake cylinder and added an RP valve that really helped. It has a 944 m/c with the 23mm bore plumbed up to the front and the 19mm to the rear. O/a the pedal feels as though there is too much travel when stationary but actually on the move it is very limited for the amount of retardation. On the rollers the MOT man was impressed. I came to the conclusion I was being too critical and fooling myself about how hard the pedal is actually pushed. The pedal pressure is quite high especially after driving a modern car but very solid feeling.

Also Deane, you have to factor in the reduction in pad movement when they have properly bedded in that is significant.

Clive
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Old March 5th 2012, 15:38
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Clive, thanks for your input - i gues it will just be a suck and see situation.

Deano
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  #10  
Old March 6th 2012, 18:44
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I've build a few 4-piston setups with stock 19mm master, and am happy with the performance and find it to be civilized. I prefer the smallest MC possible for higher line pressures and less pedal effort. For buses I use the stock single circuit MC with residual valve removed. Here's a bolt on solution for 20.6mm MC:

http://www.cip1.ca/ProductDetails.as...de=C13-16-9554

Cheers,
Lanner
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Old March 13th 2012, 14:45
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Holy crap...

http://901shop.com/main/CustomProduc...5/Default.aspx
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  #12  
Old March 19th 2012, 13:07
Turbonutta Turbonutta is offline
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im running the stock MC and im happy with it, 4 x 4 pot calipers
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  #13  
Old March 19th 2012, 18:00
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Hi

I'm running a stock 19 m/c, works great.

You might find this info useful.

Front and rear Porsche callipers on my car both use 30 &28 mm pistons

One calliper has a piston area of 2x 30 pistons = 1413.71669411541
And 2x 28 pistons = 1231.5043202072
Total piston area for one Porsche calliper = 2645.22101432261

A stock VW Beetle calliper has 2x40 mm pistons, total piston area for one calliper = 2513.27412287183

Type 3s use a 19.05 mm bore and use callipers that have 2x42 mm pistons, so total area for one calliper is = 2770.88

So a Type 3 works fine with those bore sizes, but this doesn't take into account pad area or rotor diameter.

Steve
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Old March 20th 2012, 14:32
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The thing is, you have to consider the whole fluid absorbtion, not just piston areas. In my experience sliding calipers require a lot more travel so even though the areas are less the volume required is more. 4 pots etc have a much stiffer structure and more defined seal roll back (designed to stop drag) with less travel. Once all bedded in travel required will reduce which will help. Always best to keep to the smallest you need as it will give a longer, more easily controlled, travel.
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  #15  
Old March 22nd 2012, 17:00
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'Bedding in is key'...., most complain and start messing with theory on little more than a mock up without any miles on it, RP valves are unnecessary, i have one in the rear line but its a red herring from another problem I've now rectified, IE a cracked rear disc i never thought to look for. heres my golf 20mm cylinder and RP valve, the brakes perform the same as they did with the stock 19mm cylinder and no RP valve, this is for race use, not road, its a RHD cylinder on a RHD car obviously..
here is the cracked rear disc, it was knocking the pads back away from the disc.... the more add ons you introduce away from stock, the harder it gets to sort the system, also, only add steel braided lines, if at all, after the system has been proofed out, i spent a whole season on a customers car that was braided through out, TRYING to sort the brakes out, nightmare, nothing can be clamped of to isolate problems, the pedal would hit the floor one moment then back up high 3 or 4 times every lap...
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